7970 Crossfire Rig..... potential bottleneck

[sparx1981]

Hey guys,

I've been doing some research into my setup recently and am considering swapping out my 6990 & 6970 trifire for 2x 7970s in crossfire.

Before I do this I have a could of questions.

1.) Do you think this would provide improved results compared to my current setup? I've found some rough benchmarks of 6990 vs 2x 7970 but nothing mirroring my graphic card setup. The 7970 is meant to have better scaling... plus I know that trifire doesn't scale massively well.

2.) I currently have a 1156 chipset motherboard. I know that running two cards may limit the speed that these can run... e.g. The PCIe speed will not be 16x on one card & 16x on the other. From what I've found so far though this doesn't hold back the cards too much if at all... Will the 7970 be crippled by using them on this board though? My board is a P7P55de-Pro. It supports PCIe 2.0 but obviously not 3.0. I have read that in single card usage this made no difference to the 7970 but I was wondering if it would in crossfire?

Battlefield 3 benches here are above my current setup

http://www.hardwareheaven.com/review...lefield-3.html


and unigine benches..
http://www.techpowerup.com/157741/MS...eX-Tested.html


These benches are on a different CPU but my CPU isn't appearing to limit anything right now... so my only worry is if the PCIe bus will be a factor with two 7970 cards? What do you think?

[Gilly]

It shouldn't bottleneck at that resolution, but you would really have to check for yourself, you might enjoy the saving in heat output and energy consumption anyway :D

I don't think the performance step up will be huge as you already have fast cards, but should be noticeable :)

[LeandroJVarini]

Only you for testing whether actually will performance be higher for their resolution.
In my opinion two 7970 in crossfire, will yield better than your current Trifire, did some testing in the past in setting Trifire, and a more recent VGAs for Crossfire series more new will eventually yielding more.
Already tested SLI in motherboard used 2 pci-ex to 8x SLI counter an mobo 2 PCI-ex 16x, performance from one to another was only perceived in 3D Marks for gaming performance was about 1 ~ 3% lower in the system with 2 pci-ex 8x
I saw some test pci-ex 2.0 vs 3.0 found only marketing, the same performance in games only benchs which gave a difference of 1% more in 3.0.
The VGA pci-ex 3.0 is fully compatible with a motherboard 2.0

[LeandroJVarini]

Reaview complete pci-ex 2.0 vs 3.0
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/49646-amd-radeon-hd-7970-3gb-review-13.html

[KJ128]

I was curious abou this myself and poured over forums looking to see if i was going to be wasting my time putting in another 7970 with my "aging" CPU/MOBO.
Anyway I just went for it figuring Id return the card if i was bottlenecked. Im no expert here, but given what I do understand about bottlenecks, Im in good shape. Even when my 920 at stock. I say this based on watching my CPU usage and GPU usage during (mostly) BF3 multiplayer. Specifically Gulf of Oman around 58-62 players.
Just my very non scientific, mildly informed opinion- if you have a similar setup, you shoukd be fine. I get 99% usage from both cards and arou d 50-60% usage frim my CPU. Hope this helps

[sparx1981]

I think the CPU bottleneck doesn't matter from what I've found, however the PCIe bottle neck is something I'd like to overcome at some point. As soon as I put my hard discs in RAID 0 the performance of the graphics is poor.

[Delphium]

As soon as I put my hard discs in RAID 0 the performance of the graphics is poor.

If you are not using a dedicated RAID card or rather you are using RAID provided by the motherboard then it will use the system CPU to do the work, which of cause can effect some titles.

[sparx1981]

So in theory, would this card resolve the CPU bottleneck that you mention?

RocketRaid 2320